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United. States Patent 0 M 1 3,033,894 Patented May 8, 1962 2 ative thereof, or naphthalene and cyanogen are reacted in ' 3,033,894 . the presence of a catalyst consisting essentially of an an hydrous mixture of an aluminum halide and a hydrogen halide to produce an aryl nitrile as a principal reaction . PREPARATION OF BENZIL BY CATALYZED RE ACTION OF BENZENE AND CYANOGEN William L. Fierce, Crystal Lake, and Walter J. Sandner, Carpentersville, IiL, assignors to The Pure Oil Com product in high yield. Other objects and features of this invention will become apparent ‘from time to time throughout the speci?cation pany, Chicago, 111., a corporation of Ohio N0 Drawing. Filed Dec. 23, 1957, Ser. No. 704,294 10 Claims. (Cl. 260-465) and claims as hereinafter related. This invention is based upon our discovery that aro This invention relates to new and useful improvements matic hydrocarbons, such as benzene, toluene, xylene, in processes for the preparation of aromatic 1,2-dike tones and aryl nitriles. In particular, this invention is based upon the discovery that benzil and benzonitrile may be prepared in good yield by reaction of benzene and naphthalene will react with cyanogen, in a mol ratio greater than 2:1, in the presence of a catalyst consisting of an anhydrous mixture of an aluminum halide and a hydrogen halide, to produce both an aryl nitrile and an with cyanogen in a mol ratio greater than 2:1 in the 15 intermediate compound in which the aromatic hydro presence of a molar excess of a catalyst consisting essen— carbon has added to both ends of the cyanogen molecule. tially of a mixture of an aluminum halide and a hydrogen The intermediate compound, upon hydrolysis, yields an halide. The reaction with other aromatic hydrocarbons, aromatic 1,2-diketone, such as benzil, tolil, naphthil or the like. Derivatives of aromatic hydrocarbons which such as toluene, xylene and naphthalene produces ana logous diketones and nitriles. 20 contain functional groups which are inert toward cy Benzil and analogous aromatic 1,2-diketones are useful anogen and the catalyst used react in the same way as the as chemical intermediates in the preparation of a variety aromatic hydrocarbon and are considered to be the equivalent thereof. In carrying out this reaction the the oxidation of benzoin, which is in turn prepared by con cyanogen is added in a mol ratio less than 1:2 relative densation of two molecules of benzaldehyde in the pres 25 to the aromatic hydrocarbon, and a mol ratio less than ence of an aqueous alkali cyanide solution. Aryl nitriles, 1:1 relative to the aluminum halide. These proportions such as benzonitrile (C6H5CN) and to tolunitrile of cyanogen relative to the aromatic hydrocarbon and (CH3C6H4CN), are also useful as chemical intermediates relative to the catalyst represent critical limits for the in the preparation of various organic compounds. Ben process. If the reaction is carried out using proportions zonitrile and tolunitrile are usually prepared by reaction of 30 beyond the indicated limits an entirely different product of organic compounds. Benzil is normally prepared by is obtained. The following speci?c examples illustrate the carrying out of this invention under different reac a mono-halo toluene or benzene, such as chlorotoluene or bromotoluene, or chlorobenzene or bromo-benzene, with a metal cyanide such as potassium cyanide, cuprous cya-' nide, or silver cyanide. Tolunitrile and benzonitrile may tion conditions and using different reactants. also be prepared by ammonolysis and dehydration of 35 toluic acid or benzoic acid. It is one object of this invention to provide a new and improved method for the preparation of aromatic 1,2 diketones and aryl nitriles. Another object of this invention is to provide an im proved method for the preparation of aromatic 1,2 Example I A round-bottomed ?ask equipped with a stirrer and a condenser was charged with 200 ml. of benzene and about 56 g. of anhydrous AlCl3. The mixture was stirred and a gaseous mixture of cyanogen (40 cc./min.) and 40 nitrogen (40 cc./min.) was bubbled in. The exit gas was bubbled through a dilute NaOH solution to capture any unreacted cyanogen. A total of 3.17 g. of cyanogen diketones by reaction of cyanogen and an aromatic hydro carbon. was added in 35 minutes. The reaction was maintained at ambient or room temperature. No cyanogen was Another object of this invention is to provide an im proved method for the preparation of aryl nitriles by reac found in the NaOH solution, indicating complete absorp 45 tion of cyanogen by the benzene-A1013 mixture. During tion of cyanogen and an aromatic hydrocarbon. the addition of the cyanogen the color of the reaction A feature of this invention is the provision of an im mixture gradually changed from white to yellow to orange proved process in which an aromatic hydrocarbon and to orange-red to red-brown. Next, a gaseous mixture of cyanogen are reacted in the presence of a catalyst con anhydrous HCl (60 cc./min.) and nitrogen (40 ce./min.) sisting essentially of an anhydrous mixture of an alumi 50 was bubbled into the reaction mixture. Heating was num halide and a hydrogen halide to produce an inter started and the mixture was re?uxed for 30 minutes while mediate which is hydrolyzed to produce an aromatic 1,2 the nitrogen-HCI gas mixture was bubbled into it. Then diketone. the heating and gas flow were stopped and the reaction Another feature of this invention is the provision of an improved process in which benzene, or alkali derivatives 55 mixture was allowed to cool. After standing overnight, thereof, or naphthalene is reacted with cyanogen in at the reaction mixture was poured upon a mixture of ice least a 2:1 mol ratio in the presence of a mixture of and concentrated HCl. The aqueous layer from this aluminum chloride and hydrogen chloride, at an alumi hydrolysis step was extracted with ether, which was then num chloride/cyanogen ratio greater than 1, to produce combined with the benzene layer and washed with water an intermediate product which is hydrolyzed to produce 60 until free of acid. The ether and benzene were than evaporated, leaving 7.05 g. of crude product. The pres an aromatic 1,2-diketone, such as benzil or an analogue thereof. ence of benzil in this crude material was veri?ed quali A further feature of this invention is the provision of tatively by recrystallizing a portion of it twice from an improved process in which benzene, or an alkyl deriv aqueous alcohol. Light yellow crystals were obtained 3,033,894 4 evaporated to give 100 ml. of a dark brown, liquid-solid slurry. The product was analyzed by infrared analysis which melted at 91 ° C. (pure benzil melts at 95 ° C.) . The benzil was further characterized by formation of a 2,4- . dinitrophenylhydrazone derivative which had a melting and contained p-tolunitrile in an amount equal to a yield point corresponding to the known benzil-2,4-dinitro~ phenylhydrazone derivative. The yield of the derivative, of about 65%. The remainder of the product is prin cipally p,p-dimethyl benzil, also known as tolil. 8.55 g., indicated that the yield of puri?ed product was 36.0%, and that the purity of the crude product was 65.7%. Example VI 7 In another experiment the procedure of Example I was followed except that an equal molar amount of xylene was Example II substituted for the benzene. Following this procedure a In another experiment benzil was prepared following 10 substantial amount of liquid product was obtained which substantially the same procedure used in Example I. ‘In contains a substantial yield of xylil (tetramethyl benzil) this experiment 3.34 g. of cyanogen were bubbled into and xylonitrile (dimethyl benzonitrile). the benzene-AlCL, mixture. The procedure in this case di?ered in that the I-ICl was bubbled into the reaction mixture before (instead of during) the re?uxing step. Example VII 15 In still a further experiment cyanogen and hydrogen The benzil yield in this case was slightly lower. There was, obtained 4.82 g. of crude product which produced chloride were bubbled into a suspension of aluminum chloride in a ‘solution of naphthalene in carbon disul?de. The procedure followed was substantially the same as 6.88 g. of the 2,4-dinitrophenylhydrazone derivative. The yield of derivative indicated a yield of puri?ed benzil of 20 that used in Example I. Following this procedure a sub 27.4% and a purity of 76.9% for the crude product. stantial yield of liquid product was obtained which con tains a substantial yield of dinaphthy-l diketone and naph Example III thonitrile. In still another experiment the reaction conditions were varied slightly in the preparation of benzil. In this . This process is generally operative for the preparation of aromatic 1,2-diketones and the corresponding aryl ni experiment 2.97 g. of cyanogen was bubbled into a mix ture of benzene and A1013. The procedure in this case triles. differed from the procedure of Example I in that the mix relatively inert functional substituents) may be reacted ture with aqueous H01 was re?uxed for70‘ minutes during the hydrolysis step. This change in procedure lowered the yield slightly. In this experiment 5.60 g. of crude product was obtained and converted to the 2,4-dinitro phenylhydrazone derivative. Based on the amount of the derivative obtained, the yield of pure benzil was 29.4%, and the crude product had a purity of 63.1%. In each of Examples I, II, and HI there is also obtained a ‘by-product, benzonitrile, in a yield about the same as In this process any aromatic hydrocarbon or its equivalent (derivatives of aromatic hydrocarbons having with cyanogen in the manner described above. The reac 30 tion requires an aromatic hydrocarbon-cyanogen ratio of at least 2:1 and further requires the presence of an an hydrous mixed catalyst consisting of an aluminum halide, such as aluminum chloride or aluminum bromide, and a hydrogen halide such as hydrogen chloride or hydrogen 35 rbromide. The aluminum halide catalyst must be present . in no less than an equal molar’ amount relative to the cyanogen reacted. If a lesser proportion of the aromatic hydrocarbon or the aluminum halide catalyst is used a different reaction product is obtained. In still another experiment the procedure was varied by 40 While we have described several preferred embodiments , of this invention and have described the invention fully eliminating the use of I-ICl in the reaction. In this ex and completely as required by the patent laws, we wish - periment benzene and AlCla were mixed and 3.05 g. of it understood that within the scope of the appended claims cyanogen bubbled into the mixture. The cyanogen-con this invention may be practiced otherwise than as speci?~ taining mixture was then re?uxed for 30 minutes and al ' lowed to cool. After cooling, aqueous HCl was added 45 cally described. What is claimed is: 1 to the mixture and the resulting mixture re?uxed for 70 1. A method of preparing aromatic 1,2-diketones an minutes. The aqueous layer from’ this step was extracted aryl nitriles which comprises reacting an aromatic hydro with ether and combined with the benzene layer from the carbon with cyanogen in a mol ratio ‘not less than about hydrolysis step. The combined ether and benzene solu tion was Water-washed until free of acid, and the solvent 50 72:1, in the presence of a catalyst consisting essentially of anhydrous mixture of an aluminum halide of the group was evaporated therefrom, leaving 3.09 g. of crude prod consisting of aluminum chloride and aluminum bromide uct. This product did not have the appearance of benzil and a hydrogen halide of the group consisting of hydrogen and did not melt in the range of the melting point of ben chloride and hydrogen ‘bromide vat an aluminum halide zil. Furthermore, this product did not form a derivative with 2,4-dinitrophenylhydrazone, which indicated that the 55 cyanogen molar ratio of at least 1, and hydrolyzing the reaction product to produce a mixture containing an arc product obtained in this experiment was not benzil. matic 1,2-diketone and an 'aryl nitrile. Example V 2. A method according to claim 1 in which the aromatic hydrocarbon reactant is of the group consisting of hen The preparation of tolunitrile and tolil was carried out in a 500 ml., 3-necked ?ask equipped with a gas-bubbling 60 zene, toluene, xylene, and naphthalene. 3. A method according to claim 1 in which the catalyst tube, a mercury-sealed stirrer, and a condenser. To the ’ comprises an anhydrous mixture of aluminum chloride ?ask there were charged 54 g. (0.41 mol) of anhydrous and hydrogen chloride. aluminum chloride and 2.00 ml. (1.88 mol) of QR tolu 4. A method according to claim 1 in which the aro-r ene. A gaseous mixture of cyanogen (40 cc./min.) and the yield of benzil. ' ' Example IV nitrogen (40 cc./rnin.) was bubbled in, with stirring, for 65 matic hydrocarbon is re?uxed during the reaction with 40 minutes during which time the temperature was slowly raised to 40° C. The cyanogen flow was stopped (after addition of 0.065 mol) and hydrogen chloride (75 . 1 cyanogen. 5. A method according to claim 3 in which the aro matic hydrocarbon is benzene and the reaction products comprise a mixture of benzil and benzonitrile. cc./min.) was charged with the nitrogen for additional 75 minutes (thus adding 0.23 mol of HCl). The tem 70 6. A method according to claim 3 in which the aro matic hydrocarbon is toluene ‘and the reaction products perature was gradually raised to 80° C. Then nitrogen alone was bubbled in for an additional hour. The reac tion mixture was cooled overnight and then poured on a ' are a mixture of tolil and tolunitrile. 7. A method according to claim 3 in which the aro matic hydrocarbon‘is xylene and the reaction products ob toluene layer was water-washed until neutral, ?ltered and 75 tained are a mixture of xylil and xylonitrile. mixture of ice and concentrated hydrochloric acid. The . 5 8. A method according to claim 3 in which the aro matic hydrocarbon is naphthalene in solution in an inert solvent and the reaction products are a mixture of di naphthyl 1,2-diketone and naphthyl nitrile. 9. A method according to claim 3 in which cyanogen is 5 added to a large molar excess of benzene and anhydrous aluminum chloride at ambient temperature, anhydrous hy drogen chloride is bubbled into the mixture, the mixture is re?uxed, and the product obtained is hydrolyzed with concentrated hydrochloric acid and ice to produce a mix 10 ture of benzonitn'le and benizil. 10. A method according to claim 6 for preparing tolu nitrile and tolil which comprises mixing toluene and an hydrous aluminum chloride at room temperature, bub 6 perature to about 40° C., heating the mixture of reactants to about 80° C. and bubbling anhydrous hydrogen chlo ride therethrough, and hydrolyzing the resulting reaction products to produce a mixture or“ tolil and tolunitrile. References Cited in the ?le of this patent UNITED STATES PATENTS 2,789,995 Johnston ____________ __ Apr. 23, 1957 OTHER REFERENCES Vorlander: Chemical Abstracts, vol. 5, 1911, page 3817. Migrdichian: “The Chemistry of Organic Cyanogen bling cyanogen into the mixture and increasing the tem 15 Compounds,” 1947, p. 247.